April 3 - Blue Water Shipping says a tight tidal window presented a major challenge during the recent loading of heavy pontoons and columns onto a semi-submersible ship.

The modules were loaded in Shanghai and transported to Singapore where they will form the lower hull of a semi-submersible drilling rig.

The largest pontoons measured 108 m x 16 m x 25 m and weighed 4,500 tonnes each. The dimensions of the columns are 15 m x 15 m x 20 mm and they each weighed 500 tonnes.

Blue Water Shipping was responsible for the complete project management of the shipment including the chartering of a suitable semi-submersible vessel, engineering for sea-fastening and cribbing, chartering of several tugs for the float-on operation and obtaining all permits from local authorities in China. A floating crane was deployed to undertake all the necessary lift-on operations.

Lars Skov Christensen, project manager at Blue Water Singapore says that the challenge with such a float-on operation in the Yangtze river is that the daily loading window is very narrow.

He explained that during the winter period, there is only approximately 90 minutes of slack tide before the river's current increases and it becomes unsafe to complete a float-on operation.